ACEPHALA TESTACEA. 6J L 



together; but there are several which always gape, even when brought as nigh together aa 



possible, cither at one or at both ends. 



THE FIRST FAMILY OF THE ACEPHALA TESTACEA,— 

 The Oysters, — 



Have tlie mantle open, with neither tubes nor particular apertures. They have no foot, or only a very 

 small one, and are for the most part fixed either by [cementation of] their shell, or by their byssus, to 

 rocks and to other submarine bodies. Those which are free can move only by squirting out the water 

 by a sudden closure of the valves. 



Their first section has but one muscular mass passing from one valve to the other, as we see by the 

 single impression left upon the shell. 



It is supposed that we ought to arrange here certain fossil shells, whose valves do not seem to have 

 been connected by a ligament*, but to have covered each other like a vase and its lid, and to have been 

 held together by the muscles only. They form the genus Jcardium, lirug., or Ostracite, La Perouse, 

 of which De Lamarck makes the family Riiilistes. The shells of it are thick, and of a solid or porous 

 texture. ^Ye now distinguish in it the Radiolites, Lam., whose valves are striated from the centre to 

 the circumference. One of them is flat, anil the other thick, nearly conical, and fixed. The Spheru- 

 lilcs, Lametherief, with the valves roughein d with foliations that rise up unequal!'-. And it is guessed we 

 may place here the CalceolaX, of which one valve is conical, but free, and the other flat, or even some- 

 what concave, so that they call to recollection the figure of a shoe : and the Hippuritet, with one valve 

 conical or cylindrical, that has on its inside two obtuse longitudinal crests : its base appears even to 

 have been divided into several chambers by transverse partitions ; the other valve forms, as it were, a 

 lid. The Batolifhes, Montf., are cylindrical and straight Hippuritcs ; they are often very long ; but 

 there remains much uncertainty on the nature of all these fossils. 



As to the Testaceous Acephales, known in a living state, Liumeus had united under the genus 



Ostrea (the Oysters) — 

 All those which had neither teeth nor transverse laminae in the hinge, the valves being held together by 

 a ligament lodged in a little cavity on both sides. 



The Ostrea, Brag., lias the ligament as just described, and their shells are irregular, inequivalved and foliated. 

 They are affixed to rocks, to stakes, and even to one another, by the most convex of the valves. The animal 

 (Pelorh, Foli) is one of the simplest of bivalves : we observe on it nothing remarkable but a double series of ciliie 

 round the margin of the cloak, which has the lobes united only above the head near the hinge : there is no appear- 

 ance of a foot. Every one is familiar with the common Oyster (O. edulis, Linn.), which is fished and reared in art i- 

 ticial lulls. Its fecundity is as astonishing as its taste is agreeable. [I'oli says that the ovaries of a single oyster 

 contain 1,200,000 ova.] Among the species of neighbouring countries we may notice the Ox. cristata of the Medi- 

 terranean ; among those of distant lands, the Os. paratttica, which lives itself upon the roots of the mangroves 

 and other trees that grow within the reach of the salt water ; and the Ox. /u/ in in, which i> attached by the denticu- 

 lations on the back of its convex valve, to the branches of the Gorgonia and other lithopbytes. 



\l 'le l.amarck separates, under the name of Qrypktta, certain Oysters, principally fossil, the apex of whose 

 moat convex valve projects much, and is either hookedorin some degree spiral. The other valve is often concave. 

 The greater Dumber of the species appear to have been tin-, but some of them have been seemingly attached by 

 their booked apices. We know only one recent specie- [Qriph. Irirminata). [Sowerby reunites Gryphsea to 

 iKtrca.] 



The Clams (Pecfen, Brag.) have been properly removed from the Oysters, although they have a similar binge. 

 They are easily distinguished by then- inequivalve semicircular shell being almost always regularly marked with 

 ribs, which radiate from tie- summit of each valve t.. the circumference, and furnished with two angular producl 



d MTV, that Widen the Sides of the hinge. The animal (Anius, Poll) has a small oval foot supported on a 

 cylindrical peduncle, m front of an abdomen in form of a sac hanging between the branchi.T. In son. 

 known b] Ho' Strong >nnis under their anterior ear, there is a byssus. The others are not adherent, ami can even 



swim wah considerable velocity, by flapping their valves together. The cloak li surrounded with t« waof fila- 

 ments, several of those of the exterior row being terminated by a little greenish globule [with a metallic lusl 

 The mouth Is garnished with many branched tentacula instead of the four usual labial lamina;. The shell of the 



clams is often coloured in a lively manner, [and many species are remarkable tor the ilitl. rrnce ifl colouring 



♦ [M. iv.moulini h*« raSftvmgrtd i<> |iri'vr thai laaM ibtUi ham 



ft clftfti intermediate brtwrrn ttir tliHL »« raOtpbalsi and thfl < irrho 

 irj . ».»iru tint ti.rv an true Bltralvea, 

 allied t<> Cban i lllalnville and Hang collect them Into ft dbtlBCI or- 

 der o( B " too- ol Rut 



r rM«raffltM am mabracti I ' ' ' 1 -« m -. 



tmim d! Daft 



..ril.v.nd IUiik maintain thftl lalceola li much more ntftllf 

 •Hied to Trrcbtfttulft.] 



II li J 



